package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

/**
 * A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum
 * score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries.
 * This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be
 * combined equivalently into a single search field).  We want the primary score to be the one associated with the highest boost,
 * not the sum of the field scores (as BooleanQuery would give).
 * If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching
 * another gets a higher score than "albino" matching both fields.
 * To get this result, use both BooleanQuery and DisjunctionMaxQuery:  for each term a DisjunctionMaxQuery searches for it in
 * each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery.
 * The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that
 * include this term in only the best of those multiple fields, without confusing this with the better case of two different terms
 * in the multiple fields.
 */
public class DisjunctionMaxQuery extends Query implements Iterable<Query> {

    /* The subqueries */
    private ArrayList<Query> disjuncts = new ArrayList<Query>();

    /* Multiple of the non-max disjunct scores added into our final score.  Non-zero values support tie-breaking. */
    private float tieBreakerMultiplier = 0.0f;

    /** Creates a new empty DisjunctionMaxQuery.  Use add() to add the subqueries.
     * @param tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight
     *        and added into the final score.  If non-zero, the value should be small, on the order of 0.1, which says that
     *        10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique
     *        word in the lower scored field (i.e., one that is not in any higher scored field.
     */
    public DisjunctionMaxQuery(float tieBreakerMultiplier) {
        this.tieBreakerMultiplier = tieBreakerMultiplier;
    }

    /**
     * Creates a new DisjunctionMaxQuery
     * @param disjuncts a Collection<Query> of all the disjuncts to add
     * @param tieBreakerMultiplier   the weight to give to each matching non-maximum disjunct
     */
    public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) {
        this.tieBreakerMultiplier = tieBreakerMultiplier;
        add(disjuncts);
    }

    /** Add a subquery to this disjunction
     * @param query the disjunct added
     */
    public void add(Query query) {
        disjuncts.add(query);
    }

    /** Add a collection of disjuncts to this disjunction
     * via Iterable<Query>
     */
    public void add(Collection<Query> disjuncts) {
        this.disjuncts.addAll(disjuncts);
    }

    /** An Iterator<Query> over the disjuncts */
    public Iterator<Query> iterator() {
        return disjuncts.iterator();
    }

    /**
     * Expert: the Weight for DisjunctionMaxQuery, used to
     * normalize, score and explain these queries.
     *
     * <p>NOTE: this API and implementation is subject to
     * change suddenly in the next release.</p>
     */
    protected class DisjunctionMaxWeight extends Weight {
        /** The Similarity implementation. */
        protected Similarity similarity;

        /** The Weights for our subqueries, in 1-1 correspondence with disjuncts */
        protected ArrayList<Weight> weights = new ArrayList<Weight>(); // The Weight's for our subqueries, in 1-1 correspondence with disjuncts

        /** Construct the Weight for this Query searched by searcher.  Recursively construct subquery weights. */
        public DisjunctionMaxWeight(Searcher searcher) throws IOException {
            this.similarity = searcher.getSimilarity();
            for (Query disjunctQuery : disjuncts) {
                weights.add(disjunctQuery.createWeight(searcher));
            }
        }

        /** Return our associated DisjunctionMaxQuery */
        @Override
        public Query getQuery() {
            return DisjunctionMaxQuery.this;
        }

        /** Return our boost */
        @Override
        public float getValue() {
            return getBoost();
        }

        /** Compute the sub of squared weights of us applied to our subqueries.  Used for normalization. */
        @Override
        public float sumOfSquaredWeights() throws IOException {
            float max = 0.0f, sum = 0.0f;
            for (Weight currentWeight : weights) {
                float sub = currentWeight.sumOfSquaredWeights();
                sum += sub;
                max = Math.max(max, sub);

            }
            float boost = getBoost();
            return (((sum - max) * tieBreakerMultiplier * tieBreakerMultiplier) + max) * boost * boost;
        }

        /** Apply the computed normalization factor to our subqueries */
        @Override
        public void normalize(float norm) {
            norm *= getBoost(); // Incorporate our boost
            for (Weight wt : weights) {
                wt.normalize(norm);
            }
        }

        /** Create the scorer used to score our associated DisjunctionMaxQuery */
        @Override
        public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
            Scorer[] scorers = new Scorer[weights.size()];
            int idx = 0;
            for (Weight w : weights) {
                Scorer subScorer = w.scorer(reader, true, false);
                if (subScorer != null && subScorer.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
                    scorers[idx++] = subScorer;
                }
            }
            if (idx == 0)
                return null; // all scorers did not have documents
            DisjunctionMaxScorer result = new DisjunctionMaxScorer(this, tieBreakerMultiplier, similarity, scorers, idx);
            return result;
        }

        /** Explain the score we computed for doc */
        @Override
        public Explanation explain(IndexReader reader, int doc) throws IOException {
            if (disjuncts.size() == 1)
                return weights.get(0).explain(reader, doc);
            ComplexExplanation result = new ComplexExplanation();
            float max = 0.0f, sum = 0.0f;
            result.setDescription(tieBreakerMultiplier == 0.0f ? "max of:" : "max plus " + tieBreakerMultiplier + " times others of:");
            for (Weight wt : weights) {
                Explanation e = wt.explain(reader, doc);
                if (e.isMatch()) {
                    result.setMatch(Boolean.TRUE);
                    result.addDetail(e);
                    sum += e.getValue();
                    max = Math.max(max, e.getValue());
                }
            }
            result.setValue(max + (sum - max) * tieBreakerMultiplier);
            return result;
        }

    } // end of DisjunctionMaxWeight inner class

    /** Create the Weight used to score us */
    @Override
    public Weight createWeight(Searcher searcher) throws IOException {
        return new DisjunctionMaxWeight(searcher);
    }

    /** Optimize our representation and our subqueries representations
     * @param reader the IndexReader we query
     * @return an optimized copy of us (which may not be a copy if there is nothing to optimize) */
    @Override
    public Query rewrite(IndexReader reader) throws IOException {
        int numDisjunctions = disjuncts.size();
        if (numDisjunctions == 1) {
            Query singleton = disjuncts.get(0);
            Query result = singleton.rewrite(reader);
            if (getBoost() != 1.0f) {
                if (result == singleton)
                    result = (Query) result.clone();
                result.setBoost(getBoost() * result.getBoost());
            }
            return result;
        }
        DisjunctionMaxQuery clone = null;
        for (int i = 0; i < numDisjunctions; i++) {
            Query clause = disjuncts.get(i);
            Query rewrite = clause.rewrite(reader);
            if (rewrite != clause) {
                if (clone == null)
                    clone = (DisjunctionMaxQuery) this.clone();
                clone.disjuncts.set(i, rewrite);
            }
        }
        if (clone != null)
            return clone;
        else
            return this;
    }

    /** Create a shallow copy of us -- used in rewriting if necessary
     * @return a copy of us (but reuse, don't copy, our subqueries) */
    @Override
    @SuppressWarnings("unchecked")
    public Object clone() {
        DisjunctionMaxQuery clone = (DisjunctionMaxQuery) super.clone();
        clone.disjuncts = (ArrayList<Query>) this.disjuncts.clone();
        return clone;
    }

    // inherit javadoc
    @Override
    public void extractTerms(Set<Term> terms) {
        for (Query query : disjuncts) {
            query.extractTerms(terms);
        }
    }

    /** Prettyprint us.
     * @param field the field to which we are applied
     * @return a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
     */
    @Override
    public String toString(String field) {
        StringBuilder buffer = new StringBuilder();
        buffer.append("(");
        int numDisjunctions = disjuncts.size();
        for (int i = 0; i < numDisjunctions; i++) {
            Query subquery = disjuncts.get(i);
            if (subquery instanceof BooleanQuery) { // wrap sub-bools in parens
                buffer.append("(");
                buffer.append(subquery.toString(field));
                buffer.append(")");
            } else
                buffer.append(subquery.toString(field));
            if (i != numDisjunctions - 1)
                buffer.append(" | ");
        }
        buffer.append(")");
        if (tieBreakerMultiplier != 0.0f) {
            buffer.append("~");
            buffer.append(tieBreakerMultiplier);
        }
        if (getBoost() != 1.0) {
            buffer.append("^");
            buffer.append(getBoost());
        }
        return buffer.toString();
    }

    /** Return true iff we represent the same query as o
     * @param o another object
     * @return true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
     */
    @Override
    public boolean equals(Object o) {
        if (!(o instanceof DisjunctionMaxQuery))
            return false;
        DisjunctionMaxQuery other = (DisjunctionMaxQuery) o;
        return this.getBoost() == other.getBoost() && this.tieBreakerMultiplier == other.tieBreakerMultiplier && this.disjuncts.equals(other.disjuncts);
    }

    /** Compute a hash code for hashing us
     * @return the hash code
     */
    @Override
    public int hashCode() {
        return Float.floatToIntBits(getBoost()) + Float.floatToIntBits(tieBreakerMultiplier) + disjuncts.hashCode();
    }

}
